In fact, puffer fish will be poisoned by tetrodotoxin, but its tolerance to toxin is extremely strong, which is equivalent to 1000 times that of ordinary fish. Pufferfish will secrete toxins when they are frightened, and sometimes they may poison themselves if they secrete too much.

In Doraemon Doraemon, Pang Hu doesn't feel that his singing is ugly. Doraemon commented that "you have seen puffer fish poisoned by yourself". But in fact, when the toxins secreted in the body reach a certain amount, puffer fish themselves are not spared. Tetrodotoxin is a colorless needle-like crystal, which belongs to animal alkali with acid resistance and high temperature resistance, and is one of the most toxic non-protein substances in nature. One in 50 million of them can anesthetize nerves within 30 minutes, and the minimum lethal dose to the human body is 0.5 mg. However, this extremely strong toxin can be dissolved in water and easily dissolved in dilute acetic acid, and it will begin to carbonize at 240℃. In weak alkaline solution (treated with 4% sodium hydroxide for 20 minutes), it was immediately destroyed into glucose compounds and lost its toxicity. Heating at 100℃ for 4 hours or at15℃ for 3 hours, or at 120℃ for 30 minutes, or above 200℃ for 10 minutes, can completely destroy the toxin and eliminate its toxicity.

Changes in the location and season of tetrodotoxin; the location of tetrodotoxin is the internal organs of fish. It includes the liver, gonads, intestines and stomach, blood and other parts, and its toxic content varies with different breeding environments and seasonal changes. According to the examples of the Yangtze River and the cultured river bream, the toxicity comparison of each organ is as follows: ovary → spleen → liver → blood tendon → eyes → gill rake → skin → testis → muscle. The organ toxicity of cultured river bream (over 2 years old) is consistent with that of wild river bream, but the toxin content is low.

The toxins of fugu are mainly distributed in ovary and liver, followed by kidney, blood, eyes, gills and skin. The testis and muscles are non-toxic. If the fish dies for a long time, the visceral toxins can gradually penetrate into the muscles when they are dissolved in body fluids. The amount of its toxin often varies from season to season. February to May every year is the period of ovarian development, which is highly toxic. After laying eggs from June to July, the ovaries degenerated and the toxicity was weakened. The liver is also the most toxic in spring spawning period. Therefore, whenever fresh fish are eaten in late spring and early summer, we should be especially cautious, we must choose fresh fish bodies and strictly remove internal organs to avoid poisoning.